Modifying Kernel Parameters Using a Privileged Container

Prerequisites

To access a Kubernetes cluster from a client, you can use the Kubernetes command line tool kubectl.

Procedure

Create a DaemonSet in the background, select the Nginx image, enable the Privileged Container, configure the lifecycle, and add the hostNetwork field (value: true).

Create a daemonSet file.

vi daemonSet.yaml

An example YAML file is provided as follows:

The spec.spec.containers.lifecycle field indicates the command that will be run after the container is started.

kind: DaemonSet
apiVersion: apps/v1
metadata:
  name: daemonset-test
  labels:
    name: daemonset-test
spec:
  selector:
    matchLabels:
      name: daemonset-test
  template:
    metadata:
      labels:
        name: daemonset-test
    spec:
      hostNetwork: true
      containers:
      - name: daemonset-test
        image: nginx:alpine-perl
        command:
        - "/bin/sh"
        args:
        - "-c"
        - while :; do  time=$(date);done
        imagePullPolicy: IfNotPresent
        lifecycle:
          postStart:
            exec:
              command:
              - sysctl
              - "-w"
              - net.ipv4.tcp_tw_reuse=1
        securityContext:
          privileged: true
      imagePullSecrets:
      - name: default-secret

Create a DaemonSet.
kubectl create –f daemonSet.yaml

Check whether the DaemonSet is successfully created.
kubectl get daemonset DaemonSet name

In this example, run the following command:

kubectl get daemonset daemonset-test

Information similar to the following is displayed:
```
NAME               DESIRED    CURRENT   READY    UP-T0-DATE    AVAILABLE     NODE SELECTOR   AGE
daemonset-test     2          2         2        2             2             <node>          2h
```
Query the container ID of DaemonSet on the node.
docker ps -a|grep DaemonSet name

In this example, run the following command:

docker ps -a|grep daemonset-test

Information similar to the following is displayed:
```
897b99faa9ce        3e094d5696c1                           "/bin/sh  -c while..."     31 minutes ago     Up  30 minutes  ault_fa7cc313-4ac1-11e9-a716-fa163e0aalba_0
```
Access the container.
docker exec -it containerid /bin/sh

In this example, run the following command:

docker exec -it 897b99faa9ce /bin/sh
Check whether the configured command is executed after the container is started.
sysctl -a |grep net.ipv4.tcp_tw_reuse

If the following information is displayed, the system parameters are modified successfully:
```
net.ipv4.tcp_tw_reuse=1
```